Thermal overload relay



June 21, 1960 J. B. RAMSEY ET AL 81 THERMAL OVERLOAD RELAY Filed Feb. 13, 1958 I 2 Sheets-Sheet 1 marg n-- Fig. 2 I

- INVENTORS W'TNESSES- James 8' Ramsey and Poul T. Anderson.

ATTdRNEY June 21, 1960 Fig. 3.

J. B. RAMSEY ET AL THERMAL OVERLOAD RELAY 2 Sheets-Sheet 2 United States Patent THERMAL OVERLOAD RELAY Filed Feb. 13, 1958, Ser. No. 715,004

12 Claims. (Cl. 200-113) This invention relates to thermal overload relays and, more particularly, to ambient temperature compensated overload relays.

An object ofthe invention is to provide a thermal overload relay embodying an ambient temperature compensasting element. I

Another object of the invention is to provide a thermal overload relay in which an ambient temperature responsive element is actuated by an electric current to effect opening of the relay contacts.

Another object of the invention is to provide a thermal overload relay according to the preceding paragraphs having resetting means which is readily arranged to provide either manual or automatic reclosing of the relay contacts.

A broad object of the invention is to provide a thermal overload relay that is efficient and reliable in operation, and is inexpensive to manufacture.

The invention both as to structure and operation, together with additional objects and advantages thereof, will be best understood from a study of the following detailed description of several embodiments thereof particularly when the study is made in conjunction with the accompanying drawings.

In 'saiddrawings:

Figure 1' is a vertical sectional view of a thermal overload relay embodying the principles of the invention.

Fig. 2 is plan view of the relay shown in Fig. 3.

Fig. 3 is a vertical sectional view of a thermal overload relay showing modifications of the thermally responsive bimetal element and the compensating bimetal element.

' Fig. 4 is a perspective view of a portion of the thermal overload relay showing the cover plate for controlling the resetting means.

'The thermal overload relay illustrated is of the type disclosed in our application Serial No. 499,629, filed April 6, 1955, now Patent No. 2,831,943, issued April 22, 1958, and assigned to the assignee of the present invention.

Referring to Fig. 1 of the drawing, the thermal overload relay comprises a housing having 'a lower portion, or base, 11. and an upper portion 13 both of molded insulating material. After the several parts of the relay are assembled in the housing, the two portions 11 and 13 are suitably rigidly secured together.

Mounted in the base portion 11 and secured thereto by a screw 15 is a terminal 17, the inner end of which forms a stationary contact designated as 19. A terminal 21, is secured to the base 11 at the opposite end from the terminal 17 by. a screw 23 and has its inner end formed into a bracket 25. Pivotally mounted on the bracket 25 by' means of a pin 27 is a bracket 29 to which is rigidly secured an. ambient temperature responsive bimetal ele- .spring 35 is connected under tension between the bracket .33 and a movable contact arm 37 having a movable con- 2,942,081 Patented June 21, 1960 tact 39 thereon for cooperating with the stationary contact 19. The contact arm 37 pivots in a V-shaped notch 40 in the bracket 25.

A current responsive bimetal element 41 is mounted in the upper portion 13 of the housing by means of a bracket 43 rigidly secured to the housing by 'a screw 45. One end of the bimetal 41 is rigidly secured to the bracket 43 and an adjusting screw 47, for adjusting the position of the bimetal, is threaded through the supported end of the bimetal 41 and the adjacent end of the bracket 43. An actuating rod 49 slidable in a guide opening 51 in the housing portion 13 is disposed between the free end of the current responsive bimetal 41 and the end of the compensating bimetal 31 to the left of the pivot 27.

The bimetal 41 is heated by a heater element 53 having one end secured by means of a screw 55 to a terminal 57 which, in turn, is rigidly secured to the housing portion 13 by a screw 59. The other end of the heater element 53 is similarly secured by a screw 61 to a terminal 63 which is rigidly secured to the housing portion 13 by the screw 45 which secures the bracket 43 to the housing. A resetting or reclosing rod 65 is slidably mounted in a channel in the housing portion 13 and is biased by a spring 67 having one end fixedly inserted in the housing and the other end slidably engaging in an elongated opening 69 in the reset rod 65.

When an overload current occurs in the circuit through the heater element 53, the bimetal element 41 becomes heated and when heated a predetermined amount the free end thereof bends downwardly. This movement is transmitted through the rod 49 to the compensating bimetal 31 rotating the latter counterclockwise about the pivot 27. As the bimetal 31 rotates, it carries the line of force of the overcenter spring 35 above the pivot point 40 of the contact 31 and snaps the contact arm to the open position against the lower end of the reset rod 65.

When the operating bimetal 41 cools and resumes the position shown in Fig. 1, the spring 35 moves the compensating bimetal 31 clockwise to the position shown in Fig. 1. This carries the line of force of the spring below the center line of the contact arm and snaps the contact arm to the closed position thus effecting automatic reclosing of the. contacts.

It will be noted that the resetting rod 65 is provided with an elongated opening 71 which is spaced a greater distance from the lower end of the rod 35 than the opening 69 is from the upper end of the rod 65. By reversing the reset rod 65 and inserting the end of the spring 67 in the opening 71, the spring is placed under less tension and does not move the rod down as far as shown in Fig. 1. Consequently, when the device is automatically operated in the previously described manner, the contact arm 37 is arrested inthe open position by engagement with the bracket 25. In this position, the compensating bimetal 31 does not move the end of the spring 35 far enough to cause movement of the contact arm 37 to the closed'position and the contact arm will remain in the open position until manually closed by pressing inwardly on the reset rod 65.

The high-expansion sidcs of the bimetal elements 31 and 41 are on the upper sides thereof and the bimetals have the same rate of-defiection and, hence, will deflect equally in response to changes in ambient temperature. Thus, the deflection ofjthe operating bimetal 41 required to effect opening of' the contacts remains constant.

Referring nowto Figs. 2, 3 and 4 of the drawing, which illustrate severalmodifications of the invention, the overload'thermal relay comprises a housing indicated general- 1y at 73, which is similar to the housing shown in Fig. 1. A terminal 75 extends into the housing and is secured thereto by a screw77. The terminal has a downwardly extending portion 79 on which is rigidly secured, as by a rivet 81, aspring contact member 83 having a stationary contact 85 mounted on the inner end thereof. A terminal 87 extends into the housing and is rigidly secured thereto by a screw 89. The inner portion of the terminal 87 is shaped to provide an integral bracket 91 on which is mounted the movable contact and the actuating means therefor. A contact actuating arm 93 is pivotally mounted by a pivot pin 95 on the bracket 91 and extends to the right and downwardly. An ambient temperature compensating bimetal element 97 is rigidly secured by suitable means, such as welding, to the downwardly extending free end of the actuating arm 93. A movable contact arm 99 having a movable contact 101 thereon is pivoted in a V-shaped bearing notch 103 in the bracket 91 and an overcenter spring 105 is connected under tension between the contact arm 99 and the downwardly extending portion 107 of the compensating bimetal 97 normally biasing the contact arm closed.

A thermally responsive operating bimetal element 109 has one end rigidly mounted on a bracket 111 and its other end free. The bracket 111 is rigidly secured to the housing by means of a screw 113 which also serves to secure an angular support member 115 to the housing. An adjusting screw 117 threadedly engages the support 115 and its inner end bears against the bracket 111 for the purpose of initially calibrating the relay by adjusting the'position of the bimetal element 109; After the relay is initially calibrated by the-screw 117 the access opening for the screw is filled with a sealing compound 118 to prevent tampering With the initial adjustment.

The operating bimetal 109 is disposed to be heated by a heater element 119 connected to terminals 121 and 123 by screws 125. A push rod 127 having its lower end threadedly engaging the bimetal 97 is disposed to transmit the thermal bending of the operating bimetal 109 to the compensating bimetal 97to actuate the latter and effect opening-of the contacts.

When an overload current occurs in the heater circuit, the operating bimetal I09 becornes heated and when heated a predetermined amount its free end bends downwardly engaging a shoulder 128 on the rod 127. This motion is transmitted by the rod 127 to the compensating bimetal 97 causing counterclockwise movement of the bimetal 97 and the actuating arm 93 about the pivot 95. During this movement, the-line of force of the overcenter spring 105 is moved above the pivot point 103 of the contact arm 99 and movesthe contact arm tothe open position with a snap action.

Since the adjusting screw 117 is sealed at the factory, means is provided for varying the value of overload current required to effect automatic opening of the contacts after-the relay has been placed in service. This is effected by rotating the push rod 127 which, since the rod is threaded into the compensating bimetal 97, varies the effective length of the push rod. As shown in Fig. 3, the rod 127 is provided with a reduced portion 130 which extends through an opening in the operating bimetal 109 and has a flat portion 120 at its upper end engaging in a slot 122 in the enlarged lower end portion 124 of a calibrating shaft 126. The shaft 126 is-rotatably mounted in the terminal 121 and is held in place by a snap ring 132. The upper end of the shaft is provided with a knob 134 and the shaft is biased upwardly by a-spring 136 surrounding the shaft 126 and compressed'between theheater element 119 and the underside of the knob 134.

Rotation of the "knob 134 through the connection 120-422 rotates the rod 127 which, due to the threaded engagement thereof with the bimetal 97, varies the position'ofthe shoulder '128-relative-to the operating bimetal "109 thus varyingtheoperating time of the device.

The jknob '134 also serves as a manual stop button for-effecting manual 'opening'of therelay contacts. By pressing inwardly on-the knob '134-the rod 127-is moved down-:causing counterclockwise rotation of the-compensating bimetal 97 and the actuating arm 93 about the pivot 95. This moves the line of force of the overcenter spring above the pivot point 103 of the contact arm 99 and opens the contacts as previously described. It the rod 129 is in the position, to be described later, to effect automatic reclosure, the contacts will remain open only as long as the knob 134 is held in and will automatically reclose upon release of the knob. If, however, the rod 129 is in its outer position the overcenter spring 105 will continue to bias the switch arm 99 to its open position after the knob 134 is released. Thereafter the contacts are closed, as previously described, by thrusting the reset rod 129 inwardly.

With the reset rod 129 in the position shown in Fig. 3, the opening movement of the contact arm 99 will be limited by engagement with the lower end of the reset rod. In this position, the contact arm 99 will be automatically reclosed when the operating bimetal 109 cools and resumes its normal position shown. This permits the compensating bimetal 97 under the influence of the spring 105 to resume its normal position. During this movement, the overcenter spring 105 again biases the contact arm 99 in closing direction and closes the contacts with a snap action.

Means is provided to control the reset rod 129 (Figs. 2 and 3) for either manual or automatic resetting of the contacts to the closed position. This means comprises an adjustable slide 131 which is slidably mounted onthe terminal 121 and held in adjusted position by a screw133. The slide 131 isadapted to engage in a notch 135 in the reset rod 129 in which position it limits the outward movement of the reset rod to the position shown in Fig. 3, in which position the inner end of the reset rod limits the opening movement of the contact arm 99 and provides for automatic reclosing of the contact arms as previously described. If manual resetting is desired, the slide 131 is moved out of the notch 135 to the position shown in Fig. 2, in which position the reset rod 129 is free to move out a greater distance until a shoulder 137 thereon engages 'theslide 131. With the reset rod 129 in this position, the opening movement of the contact arm 99 is stopped by engagement with the bracket 91. In this position of the contact arm 99, the spring 105 will continue to bias it open after the compensating bimetal 97 resumes its normal position shown (Fig. 3) and the contactarm is then closedby manually thrusting the reset rod 129inwardly.

Fig. 4 illustrates a diiferent way of effecting automatic or manual resetting. In this modification, terminals 139 and 141 are mounted in the top of a housing 143 and flush with the top. A reset rod 145, which is spring loaded in an upward direction, is slidably mountedadjacent one side wall of thehousing and is operable to effect resetting of mechanism of the overload relay whichmay be of the type disclosed in Fig. l. A cover plate.14.7is provided which is made of a flexible material so thatit can be snapped into position with its: ends under the terminals 139 and 141. When the cover plate 147 is assembled in the relay in theposition shown in Fig. 4, it projects into a notch 149in the edge of the reset rod 147. The notch 149 is so arranged that it permits manual operation of the reset rod to reset the relay, but retains the rod in the relay. By turning the coverplate 1 47 over and reinserting it in the relay a projection'151 is inserted in a-notch 153 inthe reset rod 145 and serves to hold the reset rod down in the automatic reset position. lndioia 155 may' be applied on the cover plate '147't0 indicate if the relay is set for hand reset or automatic reset.

The invention provides a small, compact thermal overload relay that is compensated'for changes in ambient temperature, in which the ambient temperature oompensating means is utilized to actuate thenrnovable c011- tact arm. The contact arm is actuated by'an overcenter spring which, in turn, is actuated by-the compensating bimetal. =By mounting the'compensating bimetal remotely from the operating bimetal it is less affected by the operating temperature of the relay. Thus there is provided rugged and reliable structure that is easy to assemble and inexpensive to manufacture.

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes and modifications may be made in the detail structure without departing from the spirit of the invention.

- We claim as our invention:

1. An electrical control device comprising a stationary contact and a pivoted movable contact arm having a movable contact thereon, operating means for moving said movable contact arm to open and closed positions comprising a pivoted ambient temperature responsive element, an overcenter spring normally biasing said contact arm closed and disposed to be operated by said ambient temperature responsive element to move said contact arm to the open position, and a thermally responsive element having one end supported and the other end free, actuating means disposed between movable portions of said temperature responsive elements, whereby thermal bending of said thermally responsive element in response to abnormal conditions applies a force to said compensating element to actuate said ambient temperature responsive element to cause opening movement of said contact arm.

. 2. An electrical control device comprising a stationary contact and a pivoted movable contact arm having a movable contact thereon, operating means for moving said movable contact arm to open and closed positions comprising a pivoted ambient temperature responsive element, an overcenter spring normally biasing said contact arms closed and disposed to be operated by said ambient temperature responsive bimetal element to move said contact arm to the open position, a thermally responsive element having one end supported and the other end free, and thrust transmitting means interconnecting the free end of said thermally responsive element and said ambient temperature responsive element, thermal bending of said thermally responsive element in response to abnormal conditions causing said thrust transmitting means to apply a force to said ambient temperature responsive element actuating said ambient temperature responsive element to cause opening movement of said contact arm.

3. An electrical control device comprising a stationary contact and a pivoted movable contact arm having a movable contact thereon, operating means for moving said movable contact arm to open and closed positions comprising a pivoted ambient temperature responsive bimetal element, a terminal member having an integral portion on which said ambient temperature responsive bimetal element is pivotally supported, an overcenter spring nor mally biasing said contact arm closed and operated by said ambient temperature responsive bimetal element to move said contact arm to the open position, and a thermally responsive bimetal element having one end supported and the other end free, an actuator between the free end of the thermally responsive bimetal element and a point on the ambient temperature responsive bimetal element remote from its pivot, whereby thermal bending of said thermally responsive bimetal element in response to abnormal conditions actuates said ambient temperature responsive bimetal element to cause opening movement of said contact arm.

4. An electrical control device comprising stationary contact means, a pivoted contact arm having a movable contact thereon cooperating with said stationary contact means, operating means for said contact arm comprising an ambient temperature responsive bimetal element, a terminal member having a portion on which said ambient temperature responsive bimetal element and said contact portion on one end'of said ambient temperature responsive bimetal element, a thermally responsive bimetal elementjhaving one end supported and the other end free, a push rod of insulating material disposed between the free end'of said thermally responsive bimetal element and the other end of said ambient temperature responsive bimetal element, said thermally responsive bimetal element when heated in response to overload currents bending in a direction to apply a force to said push rod to actuate said ambient temperature responsive bimetal element and cause the latter to operate said overcenter spring to effect opening movement of said contact arm.

5. An electrical control device comprising a housing of insulating material, a terminal extending into one end of said housing and having stationary contact means on the inner end thereof, a second terminal extending into the other end of said housing having support means on the inner end thereof, a movable contact arm pivotally supported on said support means, a compensating bimetal element pivotally mounted on said support means, an overcenter spring connected under tension between said contact arm and a portion of said compensating bimetal element and operable to cause opening movement of saidcontact 'arm, a thermally responsive bimetal element having one end supported and the other end free, a push rod disposed between the free end of said thermally responsive bimetal element and said compensating bimetal element operable by thermal bending of said thermally responsive bimetal element to cause compensating bi-' metal elementto operate said overcenter spring and effect opening of said contact arm.

6. An electrical control device comprising relatively movable contacts, means including an overcenter spring operable to effect opening of said contacts, a compensating element disposed to operate said overcenter spring, a pivoted member supporting said compensating element adjacent one end thereof, and a thermally responsive element, an actuator between said elements whereby said thermally responsive element is operable to effect pivotal movement of said compensating bimetal element and operation of said overcenter spring to: open said contacts.

7. An electrical control device comprising relatively movable contacts, means including an overcenter spring operable to effect opening of said contacts, a compensating bimetal element disposed to operate said overcenter spring, a pivoted member supporting said compensating bimetal element adjacent one end thereof, a thermally responsive bimetal element, an actuator between said birnetal elements, whereby said thermally responsive element is operable to effect pivotal movement of said compensating bimetal element and operation of said overcenter spring to open said contacts, means for adjusting the operating time of said device, manual means having a recess therein and operable to close said contacts, and a member insertable into said recess to lock said manual means in a position to effect automatic reclosing of said contacts.

8. An electrical control device comprising relatively movable contacts and means including an overcenter spring operable to effect opening of said contacts, a pivoted compensating bimetal element for operating said overcenter spring, a thermally responsive bimetal element operable in response to abnormal conditions, a member disposed between said bimetal elements operable by said thermally responsive bimetal element to actuate said compensating bimetal element, and means for adjusting the position of said member relative to said thermally responsive bimetal element to vary the operating time of the relay.

9. An electrical control device comprising relatively movable contacts and means including an overcenter spring operable to effect opening of said contacts, a movable ambient temperature responsive compensating element movable to operate said overcenter spring and effect opening of said contacts, a thermally responsive element pe b e in sp nse t abno ma c ndit s, a p h rod a iustab y ppo ted on d c mp sa ing elem nt n having a shoulder thereon engageable by said thermally responsive element upon thermal bending of said thermally responsive element to actuate said compensating element, and manual means for adjusting said push rod to vary the position of said shoulder relative to said thermally responsive element to thereby vary the operating time ofsaid relay.

10. An electrical control device comprising relatively movable contacts and means including an overcenter spring operable to effect opening of said co tacts, a pivoted compensating bimetal element for operating said overcenter spring, a thermally responsive bimetal element operable in response to abnormal conditions, a member disposed between said bimetal elements operable by said thermally responsive bimetal element to actuate said compensating bimetal element, and means for adjusting the Position of said member relative. to said thermally responsive bimetal element to vary the operating time of the elay s adjusting ean being also op ab to m ually actuate said compensating bimetal element to eflfect manual opening of said contacts.

, 11. An electrical control device comprising relatively movable contacts and means including an overcenter pri g op t effect pen g of sai ontact a Pi oted compensating bimetal element movable to operate said overcenter spring and effect opening of said contacts, a thermally responsive bimetal operable in response to abnormal conditions, a push rod adjustably supported on said compensating bimetal element and having a shoulder thereon engageable by said thermally responsive bime al l m t p the m ben ng of h rmally sponsive bimetal element to actuate said compensating bimetal element, and manual means for adjusting said push rod to vary the position of said shoulder relative to said thermally responsive bimetal element to thereby vary the operating time of said relay, said manual adjusting means being alsooperable to move said push rodv movable contacts and means including an overcenter spring operable to effect opening of said contacts, a pive oted compensating bimetal element disposed to operate said overcenter spring, manual means operable to actuate said compensating bimetal element to effect manual opening of said contacts, a thermally responsive bimetal element, an actuator between said bimetal elements, said thermally responsive bimetal element through said actuator being operable, in response to abnormal conditions, to actuate said compensating bimetal element to eflect automatic opening of said contacts, manual resetting means operable to engage and close said contacts, and locking means for locking said resetting means in a position to effect automatic reclosing of saidcontacts when said manual opening means is released and when said thermally responsive bimetal element cools, said manual opening means being also operable to vary the automatic operating time of said relay.

References Cited in the file of this patent UNITED STATES PATENTS 2,216,748 Lindemann Oct. 8, 19 40 2,228,523 Johnson Ian. 14, 1941 2,235,337 Shaw 2. Mar. 18, 1941 2,322,161 Schleicher June 15, 1943 2,478,503 Richmond Aug. 9, 19 49 2,653,202 Cole Sept. 22, 1 953 2,847,533 Christensen Aug, 12, 1958 2,908,786 Schleicher Oct. 13, 195.9

FOREIGN PATENTS 229,512 Switzerland Oct. 31 1943 242,726 Great Britain Nov. 19, 1925 

